WindowsPhoneCentral has leaked details of the spec via its sources near Microsoft and HTC, prior to that upcoming unveil. In terms of height and weight the device will be identical to its Android brethren, packing the same aluminum unibody that was widely praised for its premium, industrial feel.

Otherwise the spec is also an exact clone of the Android spec, with the processor being the lower end selection (vs. the MSM8974ACv3 found in some Android devices) and the internal storage being the higher end selection (vs. 16 GB found in some Android devices):

The HTC One M8 was generally praised for its pleasing metal body design, its overall solid hardware spec, and its strong battery life. The device's biggest controversy comes with the Ultrapixel duo camera that drops the physical optical image stabilization (OIS) in the first generation Ultrapixel camera, instead leaning on cruder software auto-stabilization algorithms.

The "Ultrapixel" part is also controversial as HTC has gone an unusual result and opted for bigger 2-micrometer pixels to reduce light leakage for better images in low light conditions. Most smartphone cameras, including the PureView modules found in Microsoft's Nokia Devices models, have 1.2-micrometer pixels. Hence HTC's camera has a much lower megapixel count (4 megapixels), but produces crisp, if lower-resolution images.

The HTC One W8 will reportedly share the same DotView case, which HTC's apps use to deliver updates even when the case is closed. The case simulates a dot matrix display by leaking light from the LCD display through pinholes in the case. For the HTC One W8, HTC's core apps will deliver basically an identical experience as on Android in terms of delivering the time, weather, call answering, and updates via the dot pseudo-display.

It will also add unique Windows Phone features. According to WPCentral:

This case lets you see who's calling, then answer or decline the call without opening it. Just swipe to answer or simply put it to your ear. It also shows you the date, time, weather and reminders. You can also instantly access Cortana by simply swiping down.

Some reports have indicated the HTC One M8 may receive a minor rebranding to the HTC One W8.